“I’m kind of looking forward to it,’’ she said. “It’s time for a little time apart. We’ve had enough of each other for the past 18 years.’’

Michele McDonald for The Boston Globe

Freshmen Dana and Heidi Rubenstein.

The siblings with the same birthday have had plenty of company along the way: They’re among 37 sets of twins attending Lincoln-Sudbury this year. While the 1,576-student high school has not historically tracked twins, officials said, the number may be higher this year thanks to 12 sets in the ninth grade.

But the number seems positively eye-popping compared with earlier generations. Statistics show that twin birth rates have been climbing nationally, and especially in Massachusetts, since 1980. Most recently, between 2008 and 2010, the US rate was 33.0 sets of twins per 1,000 births. In Massachusetts during that time, the rate was 44.4 per 1,000 total births, the second highest in the nation behind Connecticut.

Lincoln-Sudbury twins say it’s nice to have so many multiples in one school. It means they don’t stand out, and they have classmates who understand what it’s like to be a twin, without it being a big deal.

“If it was just my twin and I, it might seem awkward, but with so many, it seems like you’re an average classmate,’’ said 16-year-old Kevin Henderson, a sophomore.

And flying under the radar is just how his brother, Scott,
likes it.

“I don’t love a lot of attention so it’s good that there are a lot of us and people treat us the same,’’ he said.

Michele McDonald for The Boston Globe

Sophmores Kevin and Scott Henderson.

According to a National Center for Health Statistics report, issued in January 2012, that studied twin births over three decades, the incidence of multiple births in the United States was stable at about 2 percent from 1915 through the 1970s. By the early 1980s, however, twinning rates began to rise.

The rate rose by 76 percent from 1980 through 2009, going from 18.9 to 33.3 per 1,000 births. Increases in twin birth rates were evident in all 50 states, and five, including Massachusetts, reported increases of more than 100 percent.

‘I’m kind of looking forward to it. It’s time for a little time apart. We’ve had enough of each other for the past 18 years.’

Research has shown that the older age of women at childbirth accounts for about one-third of the rise in twinning over the 30 years, while the increased use of infertility treatments accounts for the other two-thirds.

Nancy L. Segal, a psychology professor and director of the Twin Studies Center at California State University Fullerton, said the twin trend appears to be continuing, though slowing down slightly with doctors are successfully implanting fewer embryos as part of infertility treatments.

At Lincoln-Sudbury this year, there are eight sets of twins in the senior class, nine in the junior class, eight in the sophomore class, and 12 in the freshman class.

The ninth-graders include
siblings who were part of an effort last year to make the Guinness Book of World Records for most twins in a single grade. The eighth-grade class at Curtis Middle School in Sudbury had 14 sets of twins, but couldn’t touch the record of 16, which was shared by three schools, in Connecticut, Illinois, and Iowa, last year.

Sudbury resident Nancy Rubenstein,
who spearheaded efforts to track the record, said she always knew there were several twins in town but didn’t realize just how many until they all attended the same middle school.

“All of a sudden they were all in school with my kids,’’ said Rubenstein, whose daughters, Heidi and Dana, 14, are now ninth-graders at the high school.

Rubenstein said she joined a support group after the twins were born, as a way to meet other moms.

“When my girls were younger, it was logistically difficult raising twins, and my involvement in the West Suburban chapter of the Massachusetts Mothers of Twins Association provided great support, as well as great friendships for both me and my kids,’’ she said. “As my twins have grown, the logistics have become more similar to those of families without twins.’’

Now, their academic and sports schedules are just like those of any other teenagers. “At this age, it’s just more of a fun thing,’’ Rubenstein said.

Her daughters said there are pros and cons associated with being part of such a large group of twins at school.

“When people first meet us, they think it’s cool,’’ Heidi said. “I like having a lot of us.’’

Dana said she loves being a twin and always having a friend who knows what’s going on in her life. She also said she wouldn’t mind if there were fewer other twins.

“It makes it a little less special,’’ she said. “I like that moment of surprise when someone sees you are a twin. But then you see the next three people are twins.’’

While the Blake siblings may be excited about heading out on their own after graduation, their mother is bracing for the change. Suzanne Blake said her son and daughter have always traveled in different social circles, but have a strong bond that she envisioned continuing after high school.

“It was always my hope they would go to the same college or at least near each other,’’ she said. “It made me sad at first, but now that they’re going in opposite directions, I know it’s definitely time.’’

Blake said it’s been an emotional few weeks for the family as the twins finished classes and geared up for graduation. It’s always hard seeing a child go off to college, but it’s more so with two, she said.

“When you don’t have other children, your empty nest starts right away in one fell swoop.’’

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Between 2008 and 2010, Massachusetts had the second highest rate of twin births in the nation.

Massachusetts44.4 per 1,000 total births

United States33.0 per 1,000total births

Sets of twins at Lincoln-Sudbury this year 37

12th grade8

11th grade 9

10th grade8

9th grade 12

SOURCES: National Vital Statistics Report for 2010, issued in August 2012; Lincoln-Sudbury Regional High School